This invention relates to a high voltage pulse generator especially useful in testing circuitry and other devices to determine resistance to electromagnetic interference (EMI). More specifically it relates to a waveform generator which has an adjustable waveform characteristic, and a waveform generator having an output whose thevenin characteristics are readily measured.
Circuits and electrical devices built for both commercial and military applications are increasingly susceptible to the harmful effects of electromagnetic interference which range from simple distortion to complete destruction. This is in part because of the trend toward lower logic signal levels in electronic systems involving sensitive devices such as microprocessors, comparitors, and gate arrays. Whether the EMI is inductive or conductive, the result is the production of voltage transients within the device of interest. Voltage transient testing techniques often include the construction of the whole system and testing it under actual conditions, which is both expensive and difficult. If the expected voltage transients can be introduced directly into the device to be tested to the degree expected to be encountered under actual conditions, the testing which results from such introduction should give a sufficient indication of stability.
Currently available devices for transient voltage waveform testing are complex and expensive. Available devices are designed to produce only one type of waveform. Consequently, a testing program which necessitates the exposure of a device to several types of transient waveforms involves the use of several devices and the concomitant connection and disconnection procedures to be used with each waveform generator. Another major dissatisfaction with currently available waveform generators is their burdensome cost. The cost of production of a device to be tested to stringent specifications is increased both by the cost of test equipment and the labor required in sequentially connecting various waveform generators to the device to be tested.
Another problem with commercially available waveform generators is the means with which the produced waveform is measured. A test waveform may have a high amplitude and a short duration output making the accurate measurement of the output difficult. The characterization of the output is important in order to insure that the specified test of the requisite severity was applied to the circuit. The additional circuitry to be added to the test device necessary to characterize the generated waveform further adds to the cost of both the waveform generator and the device being tested.
Another problem with currently available waveform generators is high internal impedance. Typically, the more complex a waveform generator is the higher its internal impedance. Therefore, the complexity necessary to produce a tailored waveform will also create unwanted internal impedance. Internal impedance mitigates the effect of the pulse on the device tested, causing the device to test to a lesser specification than desired.